The present invention relates, in general, to the field of computer systems and computer mass storage device controllers and subsystems. More particularly, the present invention relates to a system and method for determining the physical presence, proper electrical coupling and predetermined identifying characteristics and attributes of various computer system elements and components, including removable modules such as field replaceable units ("FRUs"), utilizing a minimum number of signal lines per component.
In a typical computer subsystem consisting of many fixed and removable system components such as FRUs, if a large number of signals and signal lines per device are required in order to obtain the component attributes, the total quantity of signals will ultimately represent a concomitant increase in the system cost. Moreover, a connector of sufficient size to handle such a large number of signal lines may not be either desirable or even possible in a given system.
Typical removable system components, collectively known as FRUs, are power supplies, logic cards, fans, cable interconnect modules, environmental monitoring modules, backplanes, computer mass storage devices such as disk drives and the like. In the past, identification of the various fixed and removable components in a system was done primarily by attaching labels directly to the devices themselves. As can be appreciated, it is not very practical for a system administrator or technician to manually read and record a large number of component labels to identify different types and revisions of the devices in a system. Customers and field service personnel have a real need to know what the system component attributes are as part of managing a system. It is, therefore, highly desirable to have the component information available for presentation to a remote site and to have the various component attributes accurately and automatically updated as the system is reconfigured.
For example, the component information is very useful in identifying all components of a particular revision or type and where they physically are located in the field. This is especially useful when a field recall or Field Change Order ("FCO") is necessary to correct a problem at customer locations with a particular FRU or other component. Moreover, the component attributes are also useful in managing the provision of valid system configurations. For example, if a particular power supply revision is required in order to provide higher power to a new disk drive, then it would be advantageous for the system to automatically identify that it is properly configured or that an invalid configuration exists. Monitoring, tracking and controlling product revision matrices are necessary and desirable attributes of any modern, high performance storage subsystem.
Heretofore, only relatively complex and costly methods have been considered in order to provide system component characteristics and attribute information through the use of a large number of discrete signal lines. An example of such a technique would be that 32 (2.sup.5) possible FRU revisions would require 5 binary encoded digital lines per FRU to present that information to the computer system. Likewise, if there were also 32 possible FRU types, another 5 binary encoded lines would be required per FRU to represent that information as well. To also present information as to whether or not a particular type and revision of FRU is actually physically present would require an additional 2 binary lines. Thus, a total of 12 monitoring lines per FRU would be required to present this information digitally while it is not even practical to provide information regarding whether or not the FRU monitoring lines themselves are fully functional. Moreover, in a typical enclosure having 6 FRUs, 12 monitoring lines per FRU would necessitate a total of 72 monitoring lines per enclosure.